Embodiments of the present invention relate to a substrate support for holding a substrate in a substrate processing chamber.
In the fabrication of electronic circuits and displays, semiconductor, dielectric, and electrically conducting materials are formed on a substrate, such as for example, a semiconductor wafer, ceramic or glass substrate. The materials are formed for example, by chemical vapor deposition (CVD), physical vapor deposition (PVD), ion implantation, oxidation, nitridation and other such processes. Thereafter, the deposited substrate materials can be etched to form features such as gates, vias, contact holes and interconnect lines. These processes are typically carried out in a process chamber, as for example described in commonly assigned U.S. Pat. No. 6,491,978, to Kalyanam et al., which is incorporated herein by reference in its entirety. In such processes, the substrate is placed on a substrate support and exposed to a process zone in the chamber. The support often includes a heater to further regulate the temperatures of the substrate during processing. A plasma is typically formed in the process zone by inductively or capacitively coupling energy to a process gas, or by coupling microwaves to a process gas, and this plasma processes the substrate to deposit or etch material on the substrate.
As the dimensional requirements for the layers and features formed on the substrate being increasingly smaller, the temperature uniformity across the substrate has to become more and more uniform and with narrower allowable ranges of temperatures across the substrate. For example, in CVD processes, temperature variations across the substrate surface can result in the deposition of a CVD layer having varying thickness. The tolerance range for such thickness variations becomes ever smaller as the deposited layer becomes thinner. Similarly, in etching processes different etching rates across the substrate can result in the etching of features having different shapes or sizes across the substrate. Thus it is desirable for the substrate support to minimize temperature variations across the substrate that can result in processing anomalies.
The ever-tighter temperature ranges needed across the surface of the substrate during processing is difficult to achieve with conventional supports. One conventional support comprises a chuck formed of aluminum, stainless steel, or ceramic, that has a substrate receiving surface, various vacuum ports and purge or heat transfer gas conduits, and underlying support plates. The metal pedestal and underlying support plates are welded together so that welding butt joints positioned across the surface of a plate contact an adjacent plate. In one embodiment, an electron beam is then focused on a welding butt joint to weld the butt joint to an adjacent plate. However, such conventional supports often fail to provide the desired narrow temperature range across the substrate because the electron beam weld butt joints positioned around the gas and vacuum conduits are often not smoothly or continuously welded to one another. This causes vacuum pressure or purge/heat transfer gas leakage from these joints resulting in non-uniform temperatures across the substrate. The welding process also often induces localized stresses in the plates after assembly which causes the support to warp or buckle after a number of process cycles. Warping of the plates resulting in gaps between the plates that have varying thicknesses or spacing resulting in uneven heat transfer rates from the overlying substrate and through the underlying support plates.
Another problem with conventional supports arises from their heater and vacuum port configurations. Typically, a single vacuum port is used on the support surface to hold the substrate, and this provides an uneven or even weak vacuum chucking pressure across the backside of the substrate. As a result, the substrate is more likely to pop-out when there is a fluctuation in backside pressure caused by leakage of vacuum pressure from welded joints along the vacuum path in the support. Also, excessive suction force immediately adjacent to the single port can cause the substrate to warp during processing. An improperly held substrate can also have temperature variations arising from regions having poor contact or gaps with the underlying support. Supports with built-in resistance heater elements which are not properly positioned between the plates further results in non-uniform heat applied to the overlying substrate, resulting in asymmetrical processing across the substrate.
Thus it is desirable to have a substrate support capable of maintaining the substrate at uniform and consistent temperatures and within a tight range. It is also desirable to have vacuum and gas ports and conduits that minimize loss of vacuum pressure during processing, uneven vacuum force on the substrate, and leakage of gas from joints. It is further desirable to have heaters that apply a uniform heat load to the substrate during processing.